Complex self-assembly processes require components to associate with particular partners in a preprogrammed fashion. DNA functionalization of nanoconstructs, nanoparticles, and micron-scale colloids has proven effective in getting specific cohesion between pairs of components and in forming structures. The hybridization behavior of DNA has been extensively studied for decades. Aside from genetic detection, DNA hybridization has been used to build designable DNA nano-structures, DNA-directed nano-particle structures, and micron particle structures. Such DNA engineering techniques can be utilized for DNA computing (processors), and in DNA chips, multifunctional colloidal particles as used in drug delivery, and complex colloidal self-assembly.
The highly specific, thermoreversible paired interactions that are formed by complementary DNA strands play an important role in biology and have recently been exploited as key building blocks particularly in nanotechnology as a strategy to selectively bind and create a host of potentially important structures and functional systems including crystals, motors/robots, computers, replicators, and machines. It is highly desirable to crosslink some or all of these bonds permanently for nanotechnological applications, as well as for biological assays. Several crosslinking methods have been investigated previously. Psoralen, a highly exploited crosslinking agent, intercalates between hybridized thymidine-adenosine dinucleosides in a DNA sequence and reacts with the thymines upon exposure to UV light, forming covalent links. However, the crosslinking efficiency for psoralen in solution is low (effective cross section 5×10−6 nm2) or requires a very specific attachment of the psoralen group at the start of a DNA “sticky end” next to a T-A sequence.
Cinnamate is one of the most extensively studied photo-crosslinkers used in DNA hybridization. Cinnamate-functionalized polymers are known to undergo crosslinking via photocycloaddition reactions upon exposure to UV radiation. Generally, cinnamate attaches to DNA strands using a phosphoramidite group, wherein a cinnamate on one strand is photo-crosslinked with an adjunct adenine base on another strand. However, the crosslinking efficiency is low, requiring approximately 30 minutes of incubation time for hybridization given an intensity of about 5.7 mW/cm2.
There remains, therefore, a need for efficient, specific, and permanent DNA crosslinking methods for use in biological assays, drug delivery, processors, and other nanoparticle structures.